Partially Carboxymethylated Feather Keratins. 2. Thermal and Mechanical Properties of Films

Abstract

Free cysteine thiol groups of keratin extracted from chicken feathers were partially carboxymethylated with iodoacetic acid (25-76% cysteine modification). Stable dispersions were used for the preparation of films by solution casting. Glycerol was used as a plasticizer (0.05-0.47 g/g of keratin), and films were stored at a constant relative humidity (20, 30, 50, 70, or 90%). The degree of crystallinity in the films was higher when more cysteine residues were carboxymethylated. The films displayed an optimum in mechanical properties at approximately 50% cysteine carboxymethylation. The tensile strength at this optimum was 25 MPa, the E modulus, 350 MPa, and the elongation at break, 50%. Probably, this optimum was the result of both a decreasing amount of disulfide bonds and an increasing degree of crystallinity for higher degrees of cysteine modification. The influences of a higher amount of glycerol and of different storage conditions on the mechanical properties of films from keratin with a defined degree of cysteine modification were also investigated.

Characterization and overexpression of a novel keratinase from Bacillus polyfermenticus B4 in recombinant Bacillus subtilis

“…Soft keratin has low disulfide bond content and a soft and flexible texture, and is present in skin and healing tissue, whereas hard keratin has high disulfide bond content and a hard and less flexible texture, and is present in feathers, nails, and horns (Coulombe and Omary 2002). Keratins in the hair or wool primarily contain α-helices, whereas those in feathers or nails primarily contain β-sheets (Onifade et al 1998;Schrooyen et al 2001;Wang and Parsons 1997). Cross-linking in keratin fibers occurs through disulfide bonds, hydrogen bonds, and hydrophobic interactions.…”

Thermally processed keratin films

“…Biopolymers from sustainable resources would have a distinct advantage over petroleum-derived polymers in this respect. Naturally derived proteins from gelatin, 1 soybean, 2-4 wheat, [5][6][7][8] sunflower, 9 -11 corn, [12][13][14][15][16][17][18] fish, 19 milk, 20,21 wool, 22 and poultry feather 23,24 have been processed into films using a variety of techniques. These techniques include solvent-cast and thermally processed films.…”

“…31 Most studies on processing keratin focus on reducing, or breaking, covalent sulfur-sulfur bonds to obtain a soluble fraction. 23,24 Reduction schemes require multiple chemical treatment steps, sufficient time for reaction, and subsequent processing to eliminate the chemicals used for treatment. Therefore, reduction of even small amounts of keratin proceeds on the order of hours to days.…”

“…Feather keratin has a molecular weight of about 10,500 g/mol, which corresponds to about 90 amino acids. 32 The reduced keratin has been dissolved in solvent and used to cast cohesive films for agricultural and food packaging applications 2,24 and as a protein substrate for cell culturing. 33 The advantages of using a biologically derived polymer like a protein over a synthetic polymer in these applications are obvious.…”

Isolation of a feather-degrading Bacillus subtilis strain from the alimentary tract of grebes

“…In its native state, the feather keratin is insoluble and not degradable by commonly known proteolytic enzymes such as trypsin, pepsin, and papain not only because of their tight secondary structure but also because the peptide chains are held together by disulfide linkages (Williams et al, 1990;Kim et al, 2001;Schrooyen et al, 2001). Nonetheless, feathers do not accumulate in nature and can be degraded efficiently by a myriad of microorganisms due to the action of keratinolytic proteases-keratinases (Onifade et al, 1998).…”